DWM (Dinamic Window Manager) window manager for X supports multiple workspaces and unlike ratpoison allows moving and resizing windows with the mouse.

DWM is a dynamic window manager for X. It manages windows in tiled, monocle and floating layouts. All of the layouts can be applied dynamically, optimising the environment for the application in use and the task performed.

In tiled layout windows are managed in a master and stacking area. The master area contains the window which currently needs most attention, whereas the stacking area contains all other windows. In monocle layout all windows are maximised to the screen size. In floating layout windows can be resized and moved freely. Dialog windows are always managed floating, regardless of the layout applied.

Windows are grouped by tags. Each window can be tagged with one or multiple tags. Selecting certain tags displays all windows with these tags.

Each screen contains a small status bar which displays all available tags, the layout, the number of visible windows, the title of the focused window, and the text read from the root window name property, if the screen is focused. A floating window is indicated with an empty square and a maximised floating window is indicated with a filled square before the windows title. The selected tags are indicated with a different color. The tags of the focused window are indicated with a filled square in the top left corner. The tags which are applied to one or more windows are indicated with an empty square in the top left corner.

dwm draws a small customizable border around windows to indicate the focus state.

Differences.

In contrast to ion, larswm, and wmii, dwm is much smaller, faster and simpler.

* dwm has no Lua integration, no 9P support, no shell-based configuration, no remote control, and comes without any additional tools, such as for printing the selection or warping the mouse.
* dwm is only a single binary, and its source code is intended to never exceed 2000 SLOC.
* dwm doesn’t distinguish between layers: there is no floating or tiled layer. Whether or not the clients of currently selected tag(s) are in tiled layout, you can rearrange them on the fly. Popup and fixed-size windows are always floating, however.
* dwm is customized through editing its source code, which makes it extremely fast and secure – it does not process any input data which isn’t known at compile time, except window titles and status text read from the root window’s name. You don’t have to learn Lua/sh/ruby or some weird configuration file format (like X resource files), beside C, to customize it for your needs: you only have to learn C (at least in order to edit the header file).
* Because dwm is customized through editing its source code, it’s pointless to make binary packages of it. This keeps its userbase small and elitist. No novices asking stupid questions. There are some distributions that provide binary packages though.
* dwm reads from the root window’s name to print arbitrary status text (like the date, load, battery charge). That’s much simpler than larsremote, wmiir and what not…
* NEW dwm creates a view for each Xinerama screen.

Forks and Patches.

dwm has been an influential project, many other window managers are based on dwm's source code or inspired by it. An extensive list of forks and patches can be found at the official site, a few notable examples:

xmonad is a dwm rewrite in Haskell with additional features.
awesome extends dwm with FreeType support, reconfigurability, Lua scripting support, theming, and more layout types.
echinus extends dwm with FreeType support, EWMH, click-to-focus, reconfigurability, and more layout types.
dwm-gtx is a branch of dwm, adding a 'deck' layout and better Xinerama support.
scrotwm borrows some code from dwm, adds reconfigurability and is restartable without losing state.
bug.n and HashTWM are dwm-inspired applications bringing tiling window management to Microsoft Windows systems.
cons-wm minimalist wm in scheme (not tiled)
dvtm virtual terminal manager (dwm on the console)
dwm-sprinkles dwm with colorful bar, transparency, pre-configured pertag and more
dwm-win32 dwm ported to windows
gemini terminal manager
musca inspired by dwm, more complex layout, configurable with commands, EWMH support
qtile pure python wm, used ideas from dwm
teslawm dwm fork with multihead, mouse and stdin commands support
i3 improved tiling wm